Sonar scanning method

ABSTRACT

The invention concerns a sonar installation the transmitting device of which is switchable for the transmission of sounding pulses successively in different directions, within a circular sector of angular extent n according to the direction sequence (n/2), (n/2)+ 1, (n/2)- 1, (n/2)+ 2 ...where (n/2) is the approximate center of the circular sector, the + and - signs denote directions on either side of the (n/2) direction, and the integers 1, 2, etc. represent units of angular displacement.

United States Patent inventor Dietrich Muller Achim, Germany Appl. No.842,112 Filed July 16, 1969 Patented Sept. 28, 1971 Assignee Fried.Krupp Gesellschaft mit beschrankter I-laitung Essen, Germany SONARSCANNING METHOD 2 Claims, 2 Drawing Figs.

US. Cl 340/3 R, 340/3 A, 340/5 R, 340/6 R int. Cl G0ls 9/66 Field ofSearch 340/3, 3 A,

[56] References Cited UNITED STATES PATENTS 2,925,581 2/1960 Hackley etal. 340/6 Primary ExaminerRichard A. Farley AttorneyWolf, Greenfield &Sacks ABSTRACT: The invention concerns a sonar installation thetransmitting device of which is switchable for the transmission ofsounding pulses successively in different directions, within a circularsector of angular extent n according to the direction sequence (n/2),(n/2)+l, (n/2)i, (n/2)+2 ...where (n/2) is the approximate center of thecircular sector, the and signs denote directions on either side of the(n/2) direction, and the integers l, 2, etc. represent units of angulardisplacement.

PATENIED SEP28 19m PRmk R v @ujmi In wen/or 7/9? MM MK/MI SONAR SCANNINGMETHOD The invention relates to a sonar installation, the transmittingdevice of which can be switched for the transmission of directionalsounding pulses in different directions with mutually adjoining oroverlapping directional characteristics.

In sonar installations of the said kind, there is a known procedure forachieving a high transmission level, by creating a single relativelynarrow directional beam with a high degree of compactness. and thenswinging this over the desired observation region, in steps orcontinuously. This procedure is known in the literature as RDT (RotationDirection Transmission).

In a known application of the principle, three directional transmissionbeams mutually displaced by 120 are pro duced,

by means of which the entire region of 360 can be sounded by 15 rotationof the three beams each through an angle of only I20". The advantage ofthe RDT principle, that is to say the high transmission level and theconsequently possible increase of the sounding range of the sonarinstallation, is detracted from by the large time duration which thetransmission procedure needs, and by the time differences betweenradiation of the sound in the individual directions. Since the distancemeasurement with sonar installations is based on measurement of thesound travel time, compensating devices are necessary for compensatingthe above-mentioned time differences.

Since with almost all sonar installations which use the RDT principle,the known PPI (plan position indicator) display is used for displayingthe signals from the sector being sounded,

a distorted imaging is caused if no compensation devices are provided,since echos from different directions but from objects at the samesounding distance are indicated not on a circular arc but on a spiralarc.

The spiral distortion is particularly disturbing in sonar installationsusing transmission beams displaced by 120, for objects which lie at suchan angle relative to the transmitter that they are encountered by twotransmission beams, once at the beginning of the transmitting procedureby one transmission beam and then at the end of the transmittingprocedure by the transmitting beam displaced through 120 relative to thesaid one beam. In unfavorable cases this leads to one object producingtwo separated spots on the screen of the indicating tube.

Compensation measures, which remove or reduce the above mentioneddisadvantages, are difficult to realize,

because the distance error always continuously increases and then jumpsback from its end value to its starting value.

The said disadvantages are overcome according to the in vention by atransmitting device which is successively switchable to the directions(n/2), (n/2)+l, (n/2)-l, (n/2)+2 and so on, more particularly by atransmitting assembly having m individual transmitting devices and whichthus embraces m-n different directions. The distance error, consideredover the circumference, then has in its fine structure a stepwise pathand in its coarse structure has only a continuous fluctuation betweentwo limiting values. Also in this case it can occur that an object isencountered by two neighboring transmission beams which are relativelydisplaced in time, but the displacement is however, so slight that it nolonger causes appreciable disturbances, and the PPI image isunambiguous.

In order to make the invention clearly understood, reference will now bemade to the accompanying drawings which are given by way of example andin which:

FIG. 1 illustrates the time sequence of transmission of sounding pulsesaccording to the conventional method; and

FIG. 2 illustrates the time sequence of transmission of sounding pulsesaccording to the invention.

A sonar installation with three transmission beams (la, lb, 10) whichare mutually displaced by and which can be rotated, transmits timesequential sounding pulses 2, which are propagated in the radialdirection with the speed of sound in the water. FIG. 1 shows thecondition in the water for a given instant in which in the direction 2.1a sounding pulse has been transmitted which has travelled the furthest.In the direction 2.6, of the most recently'transmitted sounding pulse,

this has not yet travelled far from the sonar installation. Thenumbering of the individual sounding pulses corresponds to the sequenceof their transmission. The described relationships are true for each ofthe other directional beams, shown displaced by 120 and 240.

Whereas FIG. 1 shows the conventional case with rotation of thedirectional transmission beams in one direction of rotation, FIG. 2shows the case according to the invention for altemate rotation inopposite directions. Assuming that the transmitting device is switchablefor the transmission of sounding pulses in different directions within acircular sector of angular extent n, the rotation should be such thatthe successive directions are (rt/2), (n/2)+l, (n/2)l, (n/2H-2 and soon. The term (n/2) represents the direction extending through theapproximate center of the sector, the and signs denote directions onopposite side of the (II/2) direction, and the integers l, 2 etc.represent units of angular displacement. For example the integer 1 mayrepresent a unit displacement of 15. The path of the distance errorwhich is now obtained by the distance difference between the soundingpulses of two neighboring directional beams, is essentially more uniformthan with the FIG. 1 arrangement.

The transmitting device may be an assembly having m individualtransmitting devices (three for the embodiment of FIG. 2) so as toembrace m-n different directions.

The invention is not limited to the illustrated example, It isapplicable to all sonar installations working according to the RDTprinciple.

We claim:

1. A method of operating a sonar transmitter to scan a sector of ndegrees, the transmitter being of the type which emits a directionalsounding pulse that covers a small segment of the sector, the methodcomprising the steps of transmitting the sequence of sounding pulses tocover the entire sector, the first sounding pulse in the sequence beingdirected along the direction (n/2) to cover a segment substantial at thecenter of the sector, and

transmitting the subsequent pulses in the sequence along directionswhich are alternately on opposite sides of the direction of transmissionof the first pulse, the subsequent pulses on the same side of thedirection of transmission of the first pulse forming an echelon ofpulses.

2. The method according to claim 1 of operating a sonar transmitter, themethod further comprising the step of concurrently employing a pluralityof transmitters of the type emitting directional sounding pulses tosimultaneous scan a plurality of sectors.

1. A method of operating a sonar transmitter to scan a sector of ndegrees, the transmitter being of the type which emits a directionalsounding pulse that covers a small segment of the sector, the methodcomprising the steps of transmitting a sequence of sounding pulses tocover the entire sector, the first sounding pulse in the sequence beingdirected along the direction (n/2) to cover a segment substantial at thecenter of the sector, and transmitting the subsequent pulses in thesequence along directions which are alternately on opposite sides of thedirection of transmission of the first pulse, the subsequent pulses onthe same side of the direction of transmission of the first pulseforming an echelon of pulses.
 2. The method according to claim 1 ofoperatinG a sonar transmitter, the method further comprising the step ofconcurrently employing a plurality of transmitters of the type emittingdirectional sounding pulses to simultaneous scan a plurality of sectors.